DiffusionVMR: Diffusion Model for Video Moment Retrieval

Video moment retrieval is a fundamental visual-language task that aims to retrieve target moments from an untrimmed video based on a language query. Existing methods typically generate numerous proposals manually or via generative networks in advance as the support set for retrieval, which is not only inflexible but also time-consuming. Inspired by the success of diffusion models on object detection, this work aims at reformulating video moment retrieval as a denoising generation process to get rid of the inflexible and time-consuming proposal generation. To this end, we propose a novel proposal-free framework, namely DiffusionVMR, which directly samples random spans from noise as candidates and introduces denoising learning to ground target moments. During training, Gaussian noise is added to the real moments, and the model is trained to learn how to reverse this process. In inference, a set of time spans is progressively refined from the initial noise to the final output. Notably, the training and inference of DiffusionVMR are decoupled, and an arbitrary number of random spans can be used in inference without being consistent with the training phase. Extensive experiments conducted on three widely-used benchmarks (i.e., QVHighlight, Charades-STA, and TACoS) demonstrate the effectiveness of the proposed DiffusionVMR by comparing it with state-of-the-art methods

K₂Sr₄(PO₃)₁₀: A Polyphosphate with Deep-UV Cutoff Edge and Enlarged Birefringence

A new polyphosphate K2Sr4(PO3)10 is synthesized by a high-temperature solution method. This compound crystallizes in the triclinic space group of P1̅, consisting of the 1D infinite [PO3]∞ chains and K and Sr ions between the chains. Compared with AM2(PO3)5 (A = K, Rb, Cs; M = Ba, Pb), K2Sr4(PO3)10 exhibits a more complex [PO3]∞ chain structure and more diverse metal cationic coordination environment. More importantly, K2Sr4(PO3)10 has both a deep-UV cutoff edge (<200 nm) and a significantly enlarged birefringence. First-principles calculations indicate that the birefringence of K2Sr4(PO3)10 is 0.017 at 1064 nm, about 2 times that of RbBa2(PO3)5 (0.008 at 1064 nm), which reaches a new height among the reported mixed alkali metal and alkaline earth metal phosphate. Theoretical calculations and structural analyses show that the enlarged birefringence of K2Sr4(PO3)10 mainly originates from the [PO3]∞ chains arranged in an inverted zigzag. This discovery introduces a new strategy for devising novel phosphate deep-UV optical crystals with a large birefringence

Peptide Self-Assemblies from Unusual α‑Sheet Conformations Based on Alternation of d/l Amino Acids

Peptide self-assembly is a hierarchical process during which secondary structures formed in the initial stages play a critical role in determining the subsequent assembling processes and final structural ordering. Unusual secondary structures hold promise as a source to develop novel supramolecular architectures with unique properties. In this work, we report the design of a new peptide self-assembly strategy based on unusual α-sheet secondary structures. In light of the strong propensity of leucine toward forming helical conformations and its high hydrophobicity, we design two short amphiphilic peptides Ac-LDLLDLK-NH2 and Ac-DLLDLLDK-NH2 with alternating l- and d-form amino acids. Microscopic imaging, neutron scattering, and spectroscopic measurements indicate that the two heterochiral peptides form highly ordered wide nanotubes and helical ribbons with monolayer thickness, in sharp contrast to twisted nanofibrils formed by the homochiral peptide Ac-LLLLK-NH2. Molecular dynamics simulations from monomers to trimers reveal that the two heteropeptides fold into α-sheets instead of β-sheets, which readily pack into tubular architectures in oligomer simulations. Simulated circular dichroism spectra based on α-sheet oligomers validate the proposed α-sheet secondary structures. These results form an important basis for the rational design of higher-order peptide assemblies with novel properties based on unusual α-sheet secondary structures